1. Field of the Invention
The present invention relates to Transaction Capabilities Application Part (TCAP) in Signaling System No. 7 (SS7) networks and, more particularly, to a method and system for improving the efficiency of the TCAP transactions.
2. Description of the Related Art
Modern telecommunication systems use an infrastructure that includes two related, but separate networks: a bearer network and a signaling network. Briefly, the bearer network carries the actual end-user voice and data traffic, while the signaling network carries the control signals that set up and release the connections in the bearer network. The signaling network uses a global signaling standard called Signaling System No. 7, or SS7, established by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). SS7 defines the procedures and protocols by which information is exchanged over the signaling network. Within an SS7 signaling network is a plurality of interconnected signaling points including service switching points (SSP), service transfer points (STP), and service control points (SCP).
Service switching points are switches that originate, terminate, or tandem calls. A service switching point sends signaling messages to other service switching points to setup, manage, and release voice circuits in the bearer network that are required to complete a call. In some cases, the service switching point may send a signaling message such as a query to the service control points.
Service control points are centralized databases or repositories of information that contain network and service information. In response to a query message, the service control point may send a message to the originating service switching point including the routing number(s) associated with the dialed number.
Service transfer points are packet switches that route network traffic between the signaling points. The service transfer points act as network hubs to provide improved utilization of the network by eliminating the need for direct links between the signaling points.
When a call is placed, the origination signaling point (typically a service switching point) sends a setup message over the signaling network to the destination signaling point to set up the call. The setup message may be routed over several intermediate signaling points (e.g., signal transfer points, signal control points) in the signaling network before arriving at the destination signaling point. Once the setup messages have been exchanged, the actual voice and data traffic for the call is then carried on voice and data channels in the bearer network. Such out-band signaling has a number of advantages, including faster call setup times (compared to in-band signaling), more efficient use of voice and data channels, support for Intelligent Network (IN) services, and generally improved security and reliability over the whole system.
In some cases, the origination signaling point may send a query to the centralized database to determine how to complete the call. Such queries may be needed, for example, to complete wireless calls (e.g., to locate the mobile unit and to authenticate subscriber information), to connect toll-free (800/888) and toll (900) calls, to carry out enhanced call features such as call forwarding, caller ID, and other Intelligent Network services. The database may respond by sending the routing numbers associated with the desired call over the signaling network back to the origination signaling point. The routing numbers allow the origination signaling point to connect the appropriate circuits in the bearer network that will correctly complete the call.
Each signaling point in the network is uniquely identified by a numeric point code. The point codes are carried in the signaling messages that are exchanged between the signaling points to identify the source and destination of each message. Based on the point codes, each signaling point selects the appropriate signaling path for each message from a routing table.
A procedure called global title translation (GTT) is used to derive the point codes from the signaling messages. Global title translation determines, for example, the Destination Point Code (DPC) from the digits present in the signaling message (e.g., the dialed 800 number, calling card number, or mobile subscriber identification number).
A graphical illustration of the SS7 protocol stack is illustrated in FIG. 1, where it can be seen that the SS7 protocol is divided into several abstract layers or levels. The first three levels define the Message Transfer Part (MTP) that makes it possible to transfer the control signals and messages in the signaling network. The lowest level, MTP level 1, defines the physical, electrical, and functional characteristics of the digital signaling links that connect the various signaling points or nodes in the signaling network together. MTP level 2 ensures accurate end-to-end transmission of a message across a signaling link including such things as flow control, message sequence validation, and error checking. MTP level 3 provides message routing between signaling points or nodes in the SS7 signaling network including re-routing traffic away from failed links and signaling points and generally controlling the signaling traffic when congestion occurs.
The ISDN User Part (ISUP) defines the protocol used to set up, manage, and release trunk circuits that carry voice and data calls over the public switched telephone network (PSTN). ISUP is used for both ISDN and non-ISDN calls. However, calls that originate and terminate on the same service switching point do not use ISUP.
The Signaling Connection Control Part (SCCP) is the transport layer for queries and service requests sent from one signaling point to another. Specifically, an SCCP connection allows messages to be addressed to specific applications at the signaling points. Each SCCP connection has a unique connection identification (CID) that is associated therewith. There are generally two types of SCCP connections: connectionless and connection-oriented.
In connectionless SCCP connections, the SCCP message does not follow a specific path, but is instead routed through the network on a signaling point to signaling point basis. Each query or service request transported on a connectionless SCCP connection requires a new SCCP connection be set up and a full SCCP routing address be used. Furthermore, global title translation is performed at each intermediate signaling point along the path.
In connection-oriented SCCP connections, the SCCP message follows a specific path defined by a logical SCCP connection. Each intermediate signaling point retains the CID of the connection and the destination point code (DPC), which is the result of global title translation. Thus, no global title translation is needed at the intermediate signaling point.
One type of message transported by an SCCP connection is a Transaction Capabilities Application Part (TCAP) message. TCAP messages are usually transported using connectionless SCCP connections. Such TCAP messages enable the deployment of advanced services such as IN services by allowing information related to the services to be exchanged between signaling points. For example, an origination signaling point (e.g., a service switching point) may use a TCAP message to query a central database (e.g., a service control point) for information regarding a toll-free call, a calling card call, a local number portabability call, and other similar services.
More importantly, TCAP messages may be used to support mobile communication systems such as the second and third generations of the Global System for Mobile Communication (GSM). The TCAP messages may be sent between mobile switching centers (MSC) and the databases associated therewith to support mobile services such as user authentication, equipment identification, and roaming. For example, when a mobile communication device (e.g., a cell phone) roams outside of its home network, it registers with a foreign network in order to continue receiving mobile services. The mobile communication device typically sends its mobile subscriber identification number to the foreign network, specifically to the visitor location register (VLR) thereof. The foreign network thereafter sends a TCAP message to the home network, specifically to the home location register (HLR) thereof. The TCAP message includes a request for authentication of the mobile communication device and any subscription information therefor. For mobile communication systems, such as GSM and UMTS, the request is based on the mobile applications part (MAP/TCAP) protocol. The home network then responds by sending a TCAP message including the result back to the foreign network to authenticate the mobile communication device.
One or more related TCAP messages are sent as part of a TCAP transaction between two signaling points. When a signaling point wishes to query another signaling point, it initiates a TCAP transaction with the second signaling point. Thereafter, the first signaling point uses that TCAP transaction to send TCAP messages related to that query to the second signaling point. Likewise, the second signaling point also initiates a TCAP transaction with the first signaling point to send TCAP messages related to the query back to the first signaling point. FIG. 2 illustrates in more detail the process of setting up a TCAP transaction from one signaling point, Node A, to another signaling point, Node B.
When an application 200a–c at Node A wishes to query another application at Node B, it initiates an application dialogue 202a–c. Examples of application dialogues 202a–c may include file transfer operations, equipment authentications, database inquiries, and the like. Each application dialogue 202a–c has a different dialogue identification (DID) that distinguishes the various application dialogues 202a–c from one another. At the TCAP layer, a TCAP transaction 204a–c is set up for each application dialogue 202a–c, and a different transaction identification (TID) is assigned to each TCAP transaction 204a–c. During the setup process, global title translation is performed for each TCAP transaction 204a–c to determine the DPC of the receiving node, for example, Node B.
In presently available telecommunication systems, there is one application dialogue 202a–c per TCAP transaction 204a–c, and there is no distinction between the application dialogues 202a–c and the TCAP transactions 204a–c. In other words, the DID becomes part of the TID. The length of the TID, however, limits the number of TCAP transactions 204a–c and, hence, the number of application dialogues 202a–c that are available to concurrent applications 200a–c. 
Accordingly, it is desirable to be able to provide a way to improve the efficiency of TCAP transactions.